1. Field of the Invention
The invention relates to a micro-catheter device utilizing .mu.J electrical discharges for the dissolution of thrombus in blood vessels, and more particularly for such treatments in the small diameter circulatory arteries of the brain in victims of stroke. It further relates to a technique for electroacoustic wave propagation against thrombus contemporaneous with high-velocity projection or jetting of pharmacologic agents against thrombus, the combination of acoustic wave or mechanical effects with pharmacologic thrombolysis being adapted to cause rapid dissolution or depolymerization of fibrin in thrombus.
2. Description of the Related Art
In the treatment of thrombus in a blood vessel, either in cardiac patients or stroke victims, conventional treatment is the intravenous administration of pharmacologic agents, such as t-PA (tissue plasminogen activator), streptokinase or urokinase. In such intravenous drug deliveries, the probability of success may be less than about 50 percent, and the success rates are limited by the fact that agents are not delivered directly to the site of the thrombus.
To ablate thrombus in an invasive procedure, various energy-based catheters have been developed, for example utilizing laser and ultrasound energy delivery systems. A disadvantage of such approaches is that the catheter's diameter may be too large, and the catheter's flexibility may be limited, thus preventing the catheter's working end from reaching the thrombus site in the small circulatory arteries of the patient's brain. Another disadvantage of such catheters is the technique associated with positioning the catheter's working end in close proximity to thrombus prior to energy delivery to have the desired effect. For example, in using a pulsed laser catheter for the ablation or photo-disruption of thrombus, the pioneering technique relied on the steady advance of the working end through the target lesion while continuously emitting pulsed laser energy. The laser's photonic energy is absorbed by the thrombus if the working end is positioned properly. Investigators found that such laser treatment could cause excessive thermal effects and damage vessel walls. More recently, the original laser-catheter technique has been modified to a "pulse-and-retreat" approach to reduce thermal effects. In other words, the laser pulses are commenced for a brief "session" just before the working end reaches the target lesion, and then the pulsing is paused for about 60 seconds before advancing the working end for another lasing "session ". The pause is adapted to allow for cooling of the vessel walls and dissipation of any gas bubbles in blood caused by the pulsed laser treatment. The disadvantages of such pulse-and-retreat" techniques are that they are time-consuming, it is difficult to effectively position the working end in relation to the thrombus prior to the initial lasing session, and it is even more difficult to position the working end prior to follow-on lasing "sessions". (See, e.g., Topaz, et al., "Acute Results, Complications, and Effect of Lesion Characteristics on Outcome With the Solid-State, Pulsed Wave, Mid-Infrared Laser Angioplasty System", Lasers in Surg. & Med. 22:228-239 (1998). Further, some such laser angioplasty treatments generally rely on photothermal absorption within the high water content of the thrombus itself to disrupt the thrombus. It would be preferable to not deliver such excessive thermal effects to intraluminal fluids and to the thrombus. In using ultrasound catheters for blood clot disruption, it is believed that an ultrasonic "radiator" comprising a piezoelectric crystal or elongate tuned member cannot easily be miniaturized to the size need for the brain's circulatory arteries and still deliver significant acoustic power. (C.function.. U.S. Pat. No. 5,318,014 to Carter titled "Ultrasonic Ablation/Dissolution Transducer").
What is needed is a micro-catheter and working end: (i)that can be miniaturized to easily introduce into 1 mm. to 3 mm. brain circulatory arteries either independently or over a guidewire; (ii) that has a lumen together with pharmacologic agent dosimetry control means for controlled delivery of such agents directly to the thrombus site; (iii) that has pharmacologic agent pressure delivery means for creating pressure gradients for such agent delivery into the working end and against thrombus, (iv) that carries acoustic-energy generation means for delivering acoustic energy against thrombus; (v) that includes control systems for modulating all parameters of both pharmacologic agent delivery pressure and acoustic energy propagation; (vi) that protects the endothelium and vessel walls from thermal damage; (vii) that protects the endothelium and vessel walls from acoustic damage while at the same time dissolving thrombus; (viii) that can be activated in a continuous mode while advancing the working end toward and through the thrombus to require less precision in the imaging component of a thrombolysis procedure; (ix) that utilizes a non-complex energy source such as electrical discharge instead of a laser source or an ultrasound generator; and (x) that provides a system with disposables that are simple and inexpensive to manufacture.